In situ tailoring of material properties in 3d printed electronics

ABSTRACT

Systems and methods for highly reproducible and focused plasma jet printing and patterning of materials using appropriate ink containing aerosol through nozzles with narrow orifice and tubes with controlled dielectric constant connected to high voltage power supply, in the presence of electric field and plasma, that enables morphological and/or bulk chemical modification and/or surface chemical modification of the material in the aerosol and/or the substrate prior to printing, during printing and post printing.

BACKGROUND OF THE INVENTION Field of the Invention

This invention relates to the field of additive printing.

Description of the Background

There is a growing need for advanced metallization techniques for 3Dinterconnects in through silicon via (TSV) and 3D integration inintegrated circuit (IC) packaging. There is also a demand for printingconductive patterns including printed circuit boards, interconnects,bumps in a range of substrates with varying glass transition temperatureand outgassing properties.

Flexible electronics, displays and wearable monitoring technologiesrequire printing of conducting materials including conducting organicsand/or metal coatings and interconnects on flexible and non-traditionalsubstrates like plastics, cellulose, polymers, textiles where theconventional techniques for metallization are difficult to apply.

Printing of porous metal structures is critical for catalysis and it isroutinely done using deposition on polymeric templates and postprocessed to remove polymers and to achieve porous structure. Theseprocesses are challenging to achieve for high throughput processing.Etching is also performed to create nanoporous surface feature.

Electrochemical deposition and electroless plating are widely used in 3Dinterconnect deposition. Magnetron sputtering, reactive sputtering,chemical vapor deposition are also used for depositing seed layer in 3Dinterconnects and through silicon via.

Photolithography, screen printing, laser induced sintering, plasmaspray, inkjet printing, aerosol printing, laser sintering are allexplored for site selective printing of metals and metal oxides.

State of the art printing technologies for printing conductive pattern,metal and metal oxide coatings are substrate dependent. Differenttechnologies must be adopted for different materials depending on theglass transition temperature, stability in vacuum (outgassing),stability in liquid medium for electroplating etc. Inkjet printing ofconductive pattern using copper nanoparticles requires post depositionannealing which limits the use of low glass transition temperatureplastics and adds additional processing steps. Screen printing is themost widely used process for planar objects, however the disadvantagesinclude resolution, organic contaminants and the need for post printthermal treatment. Thermal spray and laser induced sintering are widelyused industrial techniques in various other contexts. High oxygenconcentration, high porosity and difficulty in controlling themicrostructure are serious disadvantages of thermal spray process.Thermal spray and laser induced sintering do not provide the capabilityto tailor the material properties. For electro catalysis applications inelectro reduction of CO2 and CO, oxide-derived copper with nanocrystalline surface show promising conversion efficiency as compared tometallic copper. Thermal annealing at 500° C. for oxidation of copperand then reduction is performed to achieve the oxide derived nanocrystalline copper surface. Different technologies are needed to printthe same material with appropriate material and microstructureproperties depending on the type of application.

Atmospheric pressure plasma sintering of inkjet printed materials hasbeen reported. It involves a 2 step process (inkjet printing followed byatmospheric plasma sintering), and does not offer tailoring of materialproperties of the printed materials. Also, the use of inkjet printing inthe process severely limits the nature and type of substrates that couldbe used.

SUMMARY OF THE INVENTION

Controlled deposition of materials with tailored physical, chemical,mechanical and electronic characteristics is needed for advancedmanufacturing of electronic devices, components containing conductingmaterials, magnetic materials, dielectrics, metals and metal alloys as afunctional material. In flexible electronics, the substrates vary fromlow glass transition temperature plastics to paper-like materials whichcannot be efficiently used in well-established high vacuum based plasmadeposition process. Also, the traditional electrochemical depositionneeds a seed metal layer which is normally deposited using vacuum basedprocesses. For 3D printed electronics and flexible electronics, newprinting technologies are essential as the conventional processingtechniques are highly dependent on the type and nature of substrates.Interconnects in integrated circuits and IC packaging play a crucialrole in determining the system performance and speed. In themanufacturing of advanced interconnect for 3D IC packaging, flexibleprinted circuit boards, vertical integration, through silicon via copperfill and 3D stacking, the printing of copper interconnects withcontrolled morphology and oxidation state is essential.

Widely used screen printing technologies require pre and post processingfor enhanced adhesion and tailoring the chemical state of the materials.Hence, there is a need for advanced printing technology for flexibleelectronics and 3D printed electronics that can tailor the physical,chemical and electronic properties of the materials being deposited.

In the case of electrocatalysis for CO2 and CO reduction for airtreatment and energy conversion, the surface area of catalytic materialsis very important. Nanostructured materials with high surface area andporosity have proven to have higher conversion efficiency. There is aneed for high throughput printing technology for deposition of porousfeatures for electrocatalysis and also to plasma treatment surfaces tocreate nanostructures on surfaces.

Deposition of conducting materials including organic electronics,reduced graphene oxide and metallic coating, alloys, magnetic materials,metal oxides and ceramics with tailored surface topography, morphology,porosity, oxidation state and electronic properties are crucial for manyapplications including interconnects in integrated circuits andpackaging, flexible electronics, displays, electrodes in battery,electrocatalysis for air processing and renewable energy applications.For each of these applications, the physical and chemical state of themetal is crucial. For interconnect applications, the morphology plays akey role and the film should be non-porous and smooth. On the otherhand, for reduction electrocatalysis application in CO and CO2conversion, the nanostructured copper surface and porosity can increasethe efficiency of the conversion. For flexible electronics and displays,the stiffness and mechanical characteristics of the film is crucial.Depending on the size, shape and nature of the substrate and theapplication, an appropriate deposition process like electro plating,electroless plating, vacuum deposition, inkjet printing, laser metalsintering is used. However, in all these cases, tailoring the physicaland chemical characteristics of the film requires additional postprocessing including thermal treatment and sometimes require anadditional printing process. We have developed a substrate-independentatmospheric pressure plasma jet deposition process with ability totailor the physical, chemical and mechanical characteristics of the filmby in situ process control. The plasma jet deposition technique offersunique capability to deposit conducting materials including organics,reduced graphene oxide, metals, magnetic materials and alloys withtailored physical and chemical characteristics.

Therefore, there is presented according to the invention, systems andmethods for focused plasma jet deposition of conducting materials,including organic electronics, reduced graphene oxide, metal layersand/or metal oxide or ceramics, magnetic materials using an aerosolcontaining the appropriate material which aerosol is delivered throughnozzles connected to high voltage power supply, in the presence ofelectric field and plasma, that enables morphological and/or chemicalmodification of the metal in the aerosol prior to deposition, duringdeposition and post deposition.

The nozzle that sustains the plasma and through which themetal-containing aerosol is fed is connected to high voltage powersupply through one or more electrodes. The nozzle can be made of any orall of the following silicon wafer, quartz, glass, ceramic, plastic,machinable ceramic, glass reinforced epoxy, polyimide,polyetheretherketone, fluoropolymer, aluminum, silicon wafer containinglayers of silicon oxide and metals layers embedded on it.

The diameter of the nozzle used for deposition varies from 10 nm to 50mm. The diameter determines throughput, deposition rate, pattern sizeetc.

The electrodes connected to the nozzle to create the plasma can eitherbe externally bound or patterned and deposited to be part of the nozzleby using silicon micro machining and micro electromechanical systemsprocessing depending on the diameter requirement of the nozzle and theresolution of the metal deposition needed.

In the case of silicon micro machined nozzle, the nozzle on the siliconsubstrate can either be formed using any of the known silicon processingsteps like wet etching, dry etching, deep reactive ion etching.

The nozzle can be connected to a range of reactive and or non-reactivegases depending on the requirements.

The material in the aerosol upon entering the region in the nozzlecontaining plasma is subjected to a combined electrical field, magneticfield, electro hydrodynamic force in addition to thermal and chemicaleffects due to excitation, de-excitation and collisions in the plasma.

The morphological state, chemical structure, oxidation state, electronicstructure and magnetic state of the material can be tailored in one ormore of the following states i) in the aerosol prior to deposition, ii)on the substrate during deposition iii) on the substrate postdeposition.

The aforementioned metal layer can be deposited on semiconductor wafersincluding silicon substrates to form metal interconnects, bumps,integrated circuits, metal fill for through silicon via (TSV), contactpads and conducting layers for integrated circuit fabrication.

The metal layer can be deposited on a range of substrates includingceramics, plastics, semiconductors, metals owing to the metal layerscharacteristics including electrical conductivity, thermal conductivity,thermal cooling, etc.

Accordingly, there is provided according to an embodiment of theinvention a plasma jet printer for the in situ tailoring of materialproperties in printed electronics, comprising: nanoparticle colloid ororganic material ink input; a gas supply line for a first gas; a gassupply line for a second gas; a plasma jet printer nozzle comprising aninner tube and optionally one or more outer tubes which may or may notbe concentric with the inner tube, in which the inner and outer tubesare made of dielectric material and wherein said inner tube can have athickness or dielectric constant that is greater than, less than, or thesame as the thickness of said one or more outer tubes, and, in the casethere is one or more outer tubes, the orifice of said inner tube isinside said outer tube, in which plasma discharge is generated andsustained for tailoring material properties prior to printing, duringprinting and post printing; a manifold for controlling the gas flow tothe plasma jet nozzle; a tube for delivering said ink and said first andsecond gasses to said plasma jet printer nozzle; a plurality of metalelectrodes disposed on the outer tube of the nozzle or on the inner tubeor on both the inner and outer tubes extending along the circumferenceand connected to a high voltage power supply for generating a plasmadischarge from said nozzle; wherein the plasma discharge made ofreactive and/or non-reactive inert gases from said nozzle has ability totailor the physical, chemical, optical, magnetic, electronic propertiesand oxidation state of the bulk of the materials printed through thenozzle, prior to printing while in plasma discharge, during printing andpost printing by changing one or more of the features includingmorphology, oxidation state, chemical bonding, spin state,crystallographic structure, strain, thickness etc.; and wherein theplasma discharge characteristics are controlled by the input gas,applied voltage, nanoparticle concentration and plasma processparameters.

There is further provided according to an embodiment of the invention adevice wherein the gas used to create plasma discharge that can tailorthe material properties of printed materials may include a non-reactivegas or reactive gas or a combination of reactive and non-reactive gasesor a combination of reactive gases.

There is further provided according to an embodiment of the invention adevice wherein the non-reactive gas may include one or more of the noblegases helium, neon, argon, krypton, xenon.

There is further provided according to an embodiment of the invention adevice wherein the reactive gas may include one or more or anycombination of the following: Nitrogen, oxygen, hydrogen, carbon dioxide, acetylene, methane, air, chloride based gases, fluoride basedgases, xenon di fluoride, sulphur hexafluoride, carbon tetra fluoride,silane, siloxane, hexamethyldisiloxane, halogen, carbon, boron andsulphur based gases.

There is further provided according to an embodiment of the invention adevice wherein the print head nozzle has separate provisions, say aconcentric or a non-concentric inner nozzle through which the ink istransported by a certain gas or gas mixture and an outer nozzle thatcarries a same or different set of gas or gas mixture to enableappropriate reaction of the particles coming out of the inner nozzlewith the gas or gas mixture fed through the outer nozzle.

There is further provided according to an embodiment of the invention adevice wherein the inner and outer tubes of the print head nozzle hassame or different thickness to enable sustaining of plasma in inner andouter region independently and enable materials to get acceleratedtowards the substrate with or without altering the material properties.

There is further provided according to an embodiment of the invention adevice wherein the reactive and non reactive gases can be used i) priorto deposition ii) during deposition and iii) post deposition to createplasma discharge for tailoring material properties.

There is further provided according to an embodiment of the invention adevice wherein the materials in the aerosol carried by a non-reactiveprimary gas through the inner nozzle can be treated in-situ at theoutlet of the nozzle using a reactive secondary gas fed through theouter nozzle so that the nano materials undergo surface modificationwhile retaining the bulk properties.

There is further provided according to an embodiment of the invention adevice wherein the gas supply through the inner and/or outer nozzle,dielectric constant and thickness of the inner and outer nozzles,distribution of electrodes on the inner and outer walls of the tubes canbe appropriately chosen to get high momentum transfer to the aerosolmaterial and also used be used to get highly directional jet to printmaterials with specific geometries, patterns and properties on 2dimensional as well as 3 dimensional features.

There is further provided according to an embodiment of the invention adevice wherein the reproducibility of materials printing is ensured byreactive plasma jet cleaning of the nozzles by passing reactive gasesand generating a plasma at significantly higher potential than theoperating potential for printing so that the residues and contaminantsformed during deposition are removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the schematic of the plasma jet printer system withprovisions for the addition of various process gases to tailor thematerial properties of the nanoparticle/microparticle in the plasma jetprinter. Various process gases including helium, argon, hydrogen,nitrogen, carbon dioxide, oxygen, methane, alkane, alkene, silane,carbon tetra fluoride, sulfur hexafluoride, etc., can be used on theirown or with appropriate mixture to suit various requirements.

FIG. 1B shows the schematic of an alternate embodiment of the inventionwith provisions for the addition of various process gases to tailor thematerial properties of the nanoparticle/microparticle in the plasma jetprinter. Various process gases including helium, argon, hydrogen,nitrogen, carbon dioxide, oxygen, methane, alkane, alkene, silane,carbon tetra fluoride, sulfur hexafluoride, etc., can be used on theirown or with appropriate mixture to suit various requirements.

FIG. 2 shows through silicon via (TSV) copper fill using plasmaprocessing. Copper filling by conventional physical vapor depositioncopper filling results in void as shown in FIG. 2. Plasma jet printedcopper fill has the potential to fill the via without any voids as shownin FIG. 3.

FIG. 3 shows the cross sectional SEM image of copper deposited on asilicon wafer, and the formation of a dense film with varying surfacemorphology is observed. In situ process for controlling the oxidationstate and electronic properties of the deposited materials provides agreat advantage over any other printing process currently being used.

FIG. 4 shows an SEM image of copper nanoparticle film deposited usinghelium plasma. It is evident from the images that the nanoparticlesretain their shape and arc not undergoing physical deformation.

FIG. 5 shows SEM images of copper nanoparticle film deposited usingargon plasma. By varying the deposition time, operating voltage and thegas composition, it is possible to tailor the surface morphology fromplanar to porous structure. It is evident that the particles undergophysical deformation and form a planar film.

FIG. 6 shows SEM images of copper film deposited using coppernanoparticles by helium-t-nitrogen plasma. The images show that part ofthe nanoparticles undergo physical deformation and forms a film, whilethere are significant number of nanoparticles that retain the shape andarc embedded in the copper film.

FIG. 7 shows SEM images of porous copper film deposited using coppernanoparticles by helium, nitrogen and hydrogen mixture plasma onaluminum foil.

FIG. 8 shows SEM images of porous copper film deposited using coppernanoparticles by helium, nitrogen and hydrogen mixture plasma onsilicon.

FIG. 9 shows SEM images of planar copper film deposited using coppernanoparticles by helium, nitrogen and hydrogen mixture plasma onsilicon.

FIG. 10 shows SEM images of plasma printed copper nanoparticles and posttreated by plasma to form nanowires.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the schematic of the plasma jet printer system withprovisions for the addition of various process gases to tailor thematerial properties of the nanoparticle/microparticle in the plasma jetprinter. Various process gases including helium, argon, hydrogen,nitrogen, carbon dioxide, oxygen, methane, alkane, alkene, silane,carbon tetra fluoride, sulfur hexafluoride, etc., can be used on theirown or with appropriate mixture to suit the need.Nanoparticle/microparticle colloid input. FIG. 1 shows the followingelements:

-   -   Nanoparticle/microparticle colloid input 1    -   Gas supply line for in situ processing 2    -   Gas supply line for in situ processing 3    -   Manifold for controlling the gas flow to the plasma jet nozzle 4    -   Plasma jet printer nozzle 5    -   Nanoparticle/microparticle colloid 6 in the plasma jet printer        nozzle prior to exposure to plasma jet with particle size and        shape same as the input colloid    -   Nanoparticle/microparticle 7 in the plasma jet with physical,        chemical and electronic characteristics controlled by the input        gas, applied voltage, nanoparticle/microparticle concentration        and plasma process parameters    -   Metal electrodes 8 of the plasma jet connected to high voltage        power supply for creating the plasma discharge    -   Nanoparticle/microparticle 9 exiting the plasma jet nozzle with        tailored characteristics determined by the plasma process        parameters

The plasma jet printer consists of a tube 10 made of any one or more ofthe following: silicon, silicon wafer, quartz, glass, ceramic, plastic,machinable ceramic, glass reinforced epoxy, polyimide,polyetheretherketone, fluoropolymer, aluminum, or any other dielectricmaterial. The tube also contains two metal electrodes 8 connected tohigh voltage power supply for creating a plasma discharge in the plasmajet chamber. The high voltage power supply can be any one of thefollowing AC, DC, radio frequency, pulsed power supply. The nozzle 5,through which the material to be deposited is focused to the substrate,can be part of this tube with one end of the tube being the nozzle forprinting and another end for receiving the particle to be coated.Alternatively the nozzle, through which the material to be printed isfocused to the substrate, can also be a separate component from the tubeand connected to the tube to focus the plasma jet. The nozzle could bereplaced without having to change the tube and electrode assembly.

FIG. 1b shows the schematic of the plasma jet printer system withprovision 12 to introduce reactive and/or non reactive gases through anouter nozzle 11 with wherein the material in aerosol meets with the gasfrom outer nozzle at the exit of the inner nozzle. This will enablesurface modification of the material while retaining the bulk propertiesof the nano materials. Also, the secondary gas supply through the outernozzle 11 can be used for post treatment without having to use anadditional plasma jet printer for treatment. The secondary gas supplythrough the outer nozzle can also be used to sustain the plasma and forfocused printing, while the inner nozzle carries the materials to beprinted. This can help in increasing the momentum of the particles toget a highly directional printing.

Nonreactive, noble gases like helium, argon etc., can be used to createthe discharge as well as for printing. In order to change the chemicalcharacteristics and the electronic properties, any of the reactive gasesincluding nitrogen, oxygen, hydrogen, carbon dioxide, alkane, alkene,carbon tetra fluoride, sulfur hexafluoride etc., can be used. Thereactive and non-reactive gases can either be used on their own or withappropriate mixture of gases to obtain the required plasma processingcondition.

The material to be coated is either taken as a colloid or as a solutionand the colloid/solution is aerosolized and carried by a carrier gasinto the plasma jet tube where a plasma discharge is generated.Depending on the nature and type of nanomaterial/micromaterial/solutionused, nature and type of coating required, concentration of the materialin colloid/solution, and the nature and type of substrate used theplasma process parameters will be tailored using appropriate gasmixtures, gas flow ratios and electrical energy input for generating theplasma.

In order to change the morphology of the coating/printed materialappropriate mixture of gases, gas flow ratios, concentration andelectrical energy input are optimized to obtain either non-porous,planar coating with rough/smooth topography or porous coating withcontrolled pore size.

For example, to plasma print materials with no change in morphology andchemistry of the particles, a helium plasma with a helium flow ratevarying from 50 standard cubic centimeter (sccm) to 5000 standard cubiccentimeter (sccm), that inherently contains no filamentary discharge andlow electron density is used. In order to change the morphology of theparticles, argon plasma containing higher electron density than that ofhelium is used. The argon plasma can contain pure argon flow in therange between 50 sccm to 5000 scam or contain a mixture of helium andargon. To further increase the morphological changes, nitrogen orhydrogen with flow rate varying from 10 sccm to 3000 sccm could beintroduced in to the plasma.

The oxidation state of the material to be deposited, electronicstructure, magnetic properties, chemical structure, spin state,crystallographic structure, stress, film thickness and electronicconductivity properties can be tailored by appropriate choice of gasmixture and plasma process parameters. For changing the electronicstructure, for example to reduce the oxidation state of materials beingprinted, hydrogen gas with flow rate varying from 10 sccm to 3000 sccmmay be introduced in the plasma containing helium or argon or nitrogenor a combination of all these. Oxygen gas or clean dry air with flowrates varying from 10 sccm to 5000 sccm may be introduced for thispurpose. This will create reactive oxygen species that will interactwith the materials in the plasma or on the surface resulting inoxidation. A combination of oxygen and CF4 may be used to etch thematerial pre and post-printing. Particle shapes such as spheres, rods,plates, and wires may be used depending on the end use application. Forexample, wires may be printed to get good electrical conductivity, whilerods and plates may be used for optical applications like surfaceplasmon resonance and plasmonics.

To tune the optical properties including dielectric constant andrefractive index of the material, the hydrocarbon content and nitrogencontent in the film may be changed by introducing oxygen containing ornitrogen containing gas mixtures. To print low-k dielectric film, forexample, silicon dioxide may be printed using silane or siloxaneprecursor in addition to oxygen or clean dry air gas mixture. Toincrease the dielectric constant of the film, nitrogen gas may beintroduced in addition to silane, or siloxane or amino silane may beused so that the nitrogen incorporation in silicon dioxide increases thedielectric constant of the film.

Among the significant advantages of the present invention is the abilityto perform site selective, direct write plasma based printing ofconducting materials including conducting organic electronics, reducedgraphene oxide, conducting metallic layers, metal oxides, alloys orcomposites with controlled morphology, oxidation state and electronicstructure on flexible substrates, displays, semiconductors, plastics andenergy related materials.

Applications that require conducting materials including organics,reduced graphene oxide, metal, metal oxides, alloys or compositespreviously required to be either printed using multiple techniques withpre and/or post processing or lithography or masking can now beaccomplished with direct write plasma jet printing of the presentinvention. The direct write plasma jet printing allows chemicalstructure, oxidation state and electronic properties to be tailored insitu during the printing process by appropriate choice of gas and plasmaprocess parameters. For example, to print conducting reduced grapheneoxide pattern/film, a graphene oxide colloid may be nebulizer andintroduced into the plasma in the presence of helium or argon gas andhydrogen or nitrogen reducing gas. The reducing gas atmosphere willchange the non-conducting graphene oxide to conducting reduced grapheneoxide. The hydrogen or nitrogen reducing gas flow may vary from 10 sccmto 3000 scam.

For catalyst applications, nanostructured and porous surfaces enhancethe activity and selectivity resulting in increased efficiency. Printingof highly porous metal and metal oxide surfaces with ability for highthroughput manufacturing is a unique advantage of in situ processcontrol in plasma jet printing.

Multi-material printing and alloying capabilities with in situ processcontrol can be used for printing materials with tailored characteristicsfor bumps in integrated circuit packaging and also in displays. FIG. 2shows the application of plasma jet printer for copper filling of via inthrough silicon via semiconductor chips used in high speed processing.The copper filling in through silicon via is traditionally done by seedlayer/barrier layer deposition using vacuum based physical vapordeposition followed by electrochemical deposition of copper to fill thevia by placing the semiconductor chip in a liquid bath. The electrochemical deposited films are then polished using chemical mechanicalpolishing to remove the excess deposition. The plasma jet printer may beused to replace the electro chemical deposition and transition of thesemiconductor chips from vacuum based physical vapor deposition chamberto liquid bath for copper filling. The copper filling may be done as anin line processing followed by barrier layer deposition using physicalvapor deposition without having to go through the liquid bath baseddeposition. Plasma jet printing process provides a completely dryprocess that avoids dipping of the semiconductor chips in a liquidelectrochemical bath.

FIG. 3 shows the cross sectional SEM image of copper deposited on asilicon wafer, and the formation of a dense film with varying surfacemorphology is observed. In situ process for controlling the oxidationstate and electronic properties of the deposited materials provides agreat advantage over any other printing process currently being used.

Table 1. Elemental composition analysis of the plasma jet printed copperfilm, on silicon substrate, carried out using energy dispersive analysisby x ray spectroscopy (EDS). It is evident from Table 1 that the copperoxide can be reduced to metallic copper in situ by appropriate choice ofgas mixtures.

TABLE 1 Gas mixtures Oxidation used for state of Relative Copper OxygenCarbon Silicon plasma printing printed copper conductivity atomic %atomic % atomic % atomic % Helium Cu²⁺ Poorly 44.85 to 9.42 to 11.13 to6.61 to conducting, 70.54 14.76 14.81 27.45 Helium + metallic Highly41.14 to 0 to 0 to 0 to Nitrogen- Copper and conducting 100 30.3 28.311.16 Hydrogen Cu⁺ Argon Cu²⁺ Poorly 36.0 to 9.73 to 16.11 to 0 toconducting 82.3 25.33 30.11 28.87

The ability to change the composition of the deposited copper film by insitu treatment is shown by plasma jet printing the copper oxidenanoparticles with oxidation states of copper being 2+ and 1+ on siliconusing various gases for generating the plasma discharge and byperforming elemental quantitative analysis using energy dispersiveanalysis by x ray spectroscopy EDS. Table 1 shows the elemental analysisfor copper film deposited using helium plasma, helium plusnitrogen-hydrogen mixed plasma and argon plasma. It is evident fromTable 1 that the carbon and oxygen content in the film can be reduced to0% and increase the copper content to 100% i.e., pure metallic copper byappropriate use of gas mixtures in printing. Use of nitrogen andhydrogen gas mixture enabled reduction of copper oxide (Cu²⁺ and Cu⁺) tometallic copper (Cu).

Ability of the plasma printing to change the electronic configurationand oxidation state of materials and transition metals in particular canalso be utilized to print/achieve/tailor/magnetic properties as thechange in electronic configuration can also be associated with magneticmoment. By demonstrating tailoring the oxidation state of copper byplasma printing, one among the many transition metal oxides, theinvention may be extended to other transition metal oxides that includetitanium, iron, cobalt, nickel, manganese, zirconium etc., The magnetictransition metal oxides including iron, cobalt, manganese etc., havemultiple oxidation states including 2+, 3+ etc., and tailoring theelectronic configuration and oxidation state as described above in Table1 with a suitable gas mixture for each materials have a deep impact onthe crystallographic structure, spin state and magnetic properties ofthese materials.

The plasma discharge characteristics are controlled by the input gas,applied voltage, nanoparticle concentration and plasma processparameters. Electron density of the plasma depends on processconditions, but one prominent feature deciding the electron density ofthe plasma is the nature of gas used to generate the discharge. Theelectron densities in argon and helium are different. Argon plasma hashigher electron density than the helium plasma for the same processparameters and for atmospheric pressure plasmas the electron density inargon is 2.5 times higher than helium. The thermal conductivity of gasesalso varies. For example, the thermal conductivity of helium is higherthan that of argon and hence the substrate temperature can be changed byusing appropriate gas flow of helium and other gas mixtures. Whennitrogen is introduced into the helium plasma, the electron density,electron temperature and the current density increases. The substratetemperature may be controlled from 35° C. with pure helium flow to up to200° C. with addition of hydrogen, while the temperature remaining inbetween 35° C. to 200° C. with addition of argon or nitrogen. As aresult, the energy of the plasma varies depending on the nature and typeof gases used to generate the discharge. When thenanoparticle/microparticle colloid enters the plasma, it will besubjected to electrons, ions and radical bombardment from the plasmaspecies. As a result, the momentum the particles carry during collisionwith the substrate to form a coating varies depends on various factorsincluding the gas flow ratio, nature and type of gases, applied voltage,size and shape of the nozzle, distance between the substrate and plasmajet etc. This will have an impact on both the morphology and chemicalstructure of the material getting deposited. FIGS. 4, 5, 6, 7, 8 and 9show copper nanoparticles film, from the same set of copper oxidenanoparticle colloid, printed using atmospheric pressure plasma jetprinter using various gas mixtures. These figures show that films withvarying pattern, morphology, surface roughness and porosity can beprinted using the same set of particles and with appropriate gasmixtures.

For a given gas mixture and electrode design, the film morphology willvary depending on the externally applied voltage to generate the plasma.For example, with an applied voltage of 1 kV the plasma will have lowertemperature and electron density, and it might not have impact on themorphology of the particles. However, with an applied potential of 15kV, the plasma species will have sufficient energy to alter themorphology of the particles. For the same gas mixture, applied voltageand electrode design, the film characteristics will also be dependent onthe concentration of the particles in the colloid. For example nanomaterials with concentration of 1 mg/mL of colloid in a suspension willhave a less denser film for given time, gas mixture, applied potentialetc., than a colloid with 50 mg/ml.

FIG. 4 show SEM image of copper nanoparticle film printed using heliumplasma. It can be seen that the nanoparticles retain their shape and arenot undergoing any physical deformation to a significant extent. Theparticles are agglomerated but are mostly spherical similar to the assynthesized nanoparticles. FIG. 5 shows the SEM image of coppernanoparticle film deposited under two different process conditions. Asthe plasma density, electron density and electron temperature are higherfor argon than helium, the nanoparticles undergo physical deformationresulting in uniform film formation as shown in FIG. 5 left. Undercertain process conditions complete physical deformation and coalescenceis prevented as a result porous structure as shown in FIG. 5 right isobtained.

When nitrogen is mixed with the helium plasma, the electron density,electron temperature and the current density varies. As shown in FIG. 6the particles undergo partial physical deformation resulting in filmformation and the nanoparticles retain the shape to a certain extentresulting in film formation with particles embedded on it. By varyingthe gas ratios, applied voltage and distance between the substrate andelectrode, it is possible to increase or decrease the physicaldeformation resulting in a completely different morphology, stress andthickness.

FIGS. 7 and 8 show the copper film deposited on aluminum foil and onsilicon wafer respectively using the same set of nanoparticle colloidused with helium, argon, helium ‘nitrogen plasmas. In both substrates,it is observed that a highly porous structure is formed. Thenanoparticles undergo complete physical deformation and form a film.However, the presence of highly reactive and reducing gases in theplasma viz., nitrogen and hydrogen creates a highly porous structure. Itis also evident that a similar porous structure is also observed on boththe substrates aluminum and silicon and the process is reproducible.FIG. 9 also shows the formation of a smooth planar copper film using thesame set of nanoparticle colloid and the gas mixtures. By carefullycontrolling the gas mixtures, electron density, plasma density,operating voltage, distance between the electrode and substrate, it ispossible to control the physical deformation of the particle and as aresult control the morphology, porosity and surface roughness of thefilm.

Tailoring the morphology of surface by post-treatment is shown in FIG.10. Formation of nanowires from copper surface and copper nanoparticlesby plasma treatment with inert gas is demonstrated. Presence of hydrogenin the plasma resulted in conducting nanowire as opposed to oxides. FIG.10 shows the SEM image of plasma printed copper nanoparticle film usingargon plasma and post-treated with argon hydrogen. Formation of nanowireand spikes from the nanoparticle surface was observed which resulted inincreased physical connectivity of the printed copper by bridging thecracked portions and porous regions. Copper oxide nanowire formation oncopper through thermal oxidation has been explored widely. Surfacemorphology, temperature and treatment time will determine the uniformityof nanowires. Though the thermal oxidation and plasma oxidation resultsin copper oxide, presence of hydrogen in the plasma treatment resultedin conductive metallic copper.

Plasma jet printing for longer duration results in unwanted andinevitable deposition of materials inside the nozzle and the dielectrictube. This can affect reproducibility and reliability of the plasma jetprinter and prevent in-situ tailoring as well as plasma jet printing alltogether. The deposition of conducting materials inside the nozzleand/or the dielectric tube can severely impact the printer performance.The use of plasma offers a unique advantage by which the unwanteddeposition inside dielectric tube and the nozzle can be removed byrunning the plasma discharge without introducing the materials to beprinted into the print head and by having a plain gaseous discharge.

The plain gaseous discharge can be used to remove the materialsdeposited inside the dielectric tube along the inner circumference andinside the nozzle by one of several ways including ion bombardment, freeradical reaction, reactive ion etching etc. The gases mixture cancontain inert gases like helium, argon, etc., on their own or acombination of inert gases with reactive gases like hydrogen, oxygen,nitrogen, sulphur hexafluoride, halogen containing gases, etc. A plasmadischarge with a combination of higher potential than that used forprinting and an appropriate gas mixture as mentioned above, withoutintroducing the materials to be printed can be used to remove theunwanted material deposition inside the print head and for ensuringrepeatability and reproducibility.

Having now fully set forth the preferred embodiments and certainmodifications of the concept underlying the present invention, variousother embodiments as well as certain variations and modifications of theembodiments herein shown and described will obviously occur to thoseskilled in the art upon becoming familiar with said underlying concept.It should be understood, therefore, that the invention may be practicedotherwise than as specifically set forth herein.

1. A plasma jet printer for the in situ tailoring of material propertiesin printed electronics, comprising: a nanoparticle colloid or organicmaterial ink input; a gas supply line for a first gas; a gas supply linefor a second gas; a plasma jet printer nozzle comprising an inner tubeand optionally one or more outer tubes which may or may not beconcentric with the inner tube, in which the inner and outer tubes aremade of dielectric material and wherein said inner tube can have athickness or dielectric constant that is greater than, less than, or thesame as the thickness of said one or more outer tubes, and, in the casethere is one or more outer tubes, the orifice of said inner tube isinside said outer tube, in which plasma discharge is generated andsustained for tailoring material properties prior to printing, duringprinting and post printing; a manifold for controlling the gas flow tothe plasma jet nozzle; a tube for delivering said ink and said first andsecond gasses to said plasma jet printer nozzle; a plurality of metalelectrodes disposed on the outer tube of the nozzle or on the inner tubeor on both the inner and outer tubes extending along the circumferenceand connected to a high voltage power supply for generating a plasmadischarge from said nozzle; wherein the plasma discharge made ofreactive and/or non-reactive inert gases from said nozzle has ability totailor the physical, chemical, optical, magnetic, electronic propertiesand oxidation state of the bulk of the materials printed through thenozzle, prior to printing while in plasma discharge, during printing andpost printing by changing one or more of the features includingmorphology, oxidation state, chemical bonding, spin state,crystallographic structure, strain, thickness etc.; wherein the plasmadischarge characteristics are controlled by the input gas, appliedvoltage, nanoparticle concentration and plasma process parameters.
 2. Adevice according to claim 1, wherein the gas used to create plasmadischarge that can tailor the material properties of printed materialsmay include a non-reactive gas or reactive gas or a combination ofreactive and non-reactive gases or a combination of reactive gases
 3. Adevice as recited in claim 1, wherein the non reactive gas may includeone or more of the noble gases helium, neon, argon, krypton, xenon.
 4. Adevice as recited in claim 1, wherein the reactive gas may include oneor more or any combination of the following: Nitrogen, oxygen, hydrogen,carbon di oxide, acetylene, methane, air, chloride based gases, fluoridebased gases, xenon di fluoride, sulphur hexafluoride, carbon tetrafluoride, silane, siloxane, hexamethyldisiloxane, halogen, carbon, boronand sulphur based gases.
 5. A device as recited in claim 1, wherein theprint head nozzle has separate provisions, say a concentric or anon-concentric inner nozzle through which the ink is transported by acertain gas or gas mixture and an outer nozzle that carries a same ordifferent set of gas or gas mixture to enable appropriate reaction ofthe particles coming out of the inner nozzle with the gas or gas mixturefed through the outer nozzle.
 6. A device as recited in claim 1, whereinthe inner and outer tubes of the print head nozzle has same or differentthickness to enable sustaining of plasma in inner and outer regionindependently and enable materials to get accelerated towards thesubstrate with or without altering the material properties.
 7. A deviceas recited in claim 1, wherein the reactive and non reactive gases canbe used i) prior to deposition ii) during deposition and iii) postdeposition to create plasma discharge for tailoring material properties.8. A device as recited in claim 1, wherein the materials in the aerosolcarried by a non-reactive primary gas through the inner nozzle can betreated in-situ at the outlet of the nozzle using a reactive secondarygas fed through the outer nozzle so that the nano materials undergosurface modification while retaining the bulk properties.
 9. A device asrecited in claim 1, wherein the gas supply through the inner and/orouter nozzle, dielectric constant and thickness of the inner and outernozzles, distribution of electrodes on the inner and outer walls of thetubes can be appropriately chosen to get high momentum transfer to theaerosol material and also used be used to get highly directional jet toprint materials with specific geometries, patterns and properties on 2dimensional as well as 3 dimensional features.
 10. A device as recitedin claim 1, wherein the reproducibility of materials printing is ensuredby reactive plasma jet cleaning of the nozzle, dielectric tube and/orprint head by passing reactive gases and generating a plasma atsignificantly higher potential than the operating potential for printingso that the residues and contaminants formed during deposition areremoved.
 11. A method for removing unwanted materials deposited insidethe nozzle and/or dielectric tube of a plasma jet printer comprisingrunning a plasma discharge through said nozzle and/or dielectric tubewithout introducing materials to be printed.
 12. A method according toclaim 11, wherein said plasma discharge that is higher than a plasmadischarge used for printing.
 13. A method according to claim 11, furthercomprising ion bombardment, free radical reaction and/or reactive ionetching.